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Course: MCAT > Unit 4

Lesson 1: Foundations of behavior passages

Stress responses and the endocrine system


The world offers a variety of stressors to its inhabitants, and as humans, we respond to our stressful world through an internally coordinated response, often referred to as behavior.
Stress that is physical in nature might result in tissue damage, eliciting pain stimuli that are transmitted to the median eminence of the hypothalamus. Once it has been stimulated, the hypothalamus secretes corticotropin-releasing hormone (CRH) into the hyphophyseal portal system. CRH then stimulates the production of adrenocorticopic hormone (ACTH) by the pituitary. This cascading reaction results in the rapid rise in circulating cortisol. Mental stress has also been shown to rapidly increase ACTH secretion. Scientists believe this is the result of increased activity in the limbic system, namely the hippocampus and amygdala, which signal the medial hypothalamus in response to stimulation.
To further examine the impact of stress, a researcher decides to investigate the levels of blood corticosterone (the physiological equivalent of cortisol in rats) in rats who have experienced a physiological stressor, tibia and fibula fracture. Figure 1 outlines one rat’s corticosterone levels following the fracture.
Figure 1
What effect do increasing levels of thyroid hormone have on oxygen consumption rates in tissue?
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